Old links apparently weren’t necessarily updated when the forum software here was last migrated. As Qstor2 suggested two comments (and six years) before yours, use the general “Search forums” mechanism in (what is currently) the white stripe near the top of the page to find the current location of whatever it is that you’re seeking.
There are two upgrades that broke links... once in about 2008, and the recent one when we moved from VB to XenForo. The newer VB wouldn't read the data, so we were unable to upgrade, and XenForo was at least able to get the messages across.
Seems to me XenForo maintained the thread ids, and it should be straight forward to have a handler that redirects those legacy links to the current thread. Odd that they don't provide that feature.